A starting point for the invention has been a centrifugal separator, which has a rotor for rotation around a central axis extending through the rotor and in which
a rotor body, which comprises a first end wall and a second end wall arranged axially one on each side of a separation chamber surrounding the rotor axis, forms a central inlet for said liquid containing the suspended light and heavy particles, a central first outlet through said first end wall for liquid having been freed from light and heavy particles and a central second outlet for a liquid light phase containing separated light particles, PA1 a stack of conical separation discs is arranged in the separation chamber in a way such that the separation discs, which have base portions and apex portions and are arranged spaced from each other, are arranged coaxially with the rotor and have their apex portions facing said first end wall, PA1 each one of several inlet channels, which are distributed around the central axis and which connect the central inlet of the rotor body with the separation chamber, has an inclination relative to the central axis in the same direction as a generatrix of each one of the conical separation disc, PA1 the separation discs have several series of aligned holes forming several parallel distribution channels through said stack, which communicate with the inter-spaces between the separation discs and at their ends situated closest to said first end wall communicate with said inlet channels, and PA1 each one of a number of outlet channels, which are distributed around the rotor axis and intended for liquid having been freed from light and heavy particles, has a channel opening situated in the separation chamber close to said first end wall and extending from said channel opening towards the rotor axis. PA1 that said inlet channels open in a counter pressure chamber extending around the rotor axis and limited axially by chamber walls which are substantially free of rotational entraining members, so that liquid is admitted to rotate in the counter pressure chamber at an angular velocity smaller than that of the rotor body, PA1 that the counter pressure chamber has a first part communicating with said distribution channels and a second part situated radially outside the said first part and communicating with at least one sludge passage, and PA1 that said sludge passage communicates with the separation chamber in a part thereof so situated that separated heavy particles are admitted to move from the sludge passage radially outwardly in the separation chamber through an area thereof situated axially and/or radially outside a space, which surrounds the stack of separation discs and through which liquid having been freed from suspended light particles has to flow on its way from the interspaces between the separation discs to the openings of said outlet channels.
A centrifugal separator of this kind, known for instance from SE-19 666 and SE-21 885 (both granted in 1904), has certain advantages over other centrifugal separators. One advantage lies in the fact that liquid to be treated in the centrifugal separator is introduced into the separation chamber of the rotor at the rotor end wall faced by the apex portion of the separation discs. This makes possible an effective use from a separation point of view of said inlet channels, which extend between the central inlet of the rotor and the so called distribution channels in the stack of separation discs. Thus, thanks to the inclination of these inlet channels in relation to the rotor axis, the pre-separation of the liquid obtained in the inlet channels may be used to a maximum, i.e. the result of this pre-separation is not spoiled by an undesired cross-flow of the part flows of the liquid, which are obtained through the pre-separation, when this liquid is conducted further into said distribution channels. A cross-flow of this kind would be obtained, however, if the liquid would be conducted into the distribution channels at the opposite end of the separation disc stack after having flowed through corresponding inlet channels having the same inclination relative to the central axis in this part of the rotor.
Another advantage of a centrifugal separator of the described kind is that liquid conducted into the separation chamber in the above described manner can preferably be supplied to the rotor through the rotor body end wall at which said inlet channels are situated. Thus, the liquid need not be conducted axially through the whole of the rotor before it enters the separation chamber, which most often happens today in centrifugal rotors having frusto-conical separation discs. This is advantageous particularly in connection with rotors having relatively small dimensions and having their respective two end walls kept together axially by means of force absorbing members arranged centrally in the rotor.